1. Field of the Invention
This invention relates to new polyester amide compositions having utility as fabric adhesives. More particularly, it relates to novel polyester amides derived from terephthalic acid, 1,6-hexanediol, 1,6-hexanediamine and dicarboxylic acids having 4 to 12 carbon atoms.
2. Description of the Prior Art
Patents relating to the use of synthetic polyesters for use as fabric adhesives include U.S. Pat. Nos. 4,094,721 and 3,948,859. These patents generally suggest that for a composition to function as a fabric adhesive, it should have a relatively low melting point and a relatively rapid rate of crystallization. The final bond should also be sufficiently crystalline that it is not softened by dry cleaning solvents.
It has now been found that polyester amide compositions having a suitable level of melting point, adhesive bond strength, solvent resistance, and set-up time can be produced. It is well known that polyesters can be used as fabric adhesives by proper modification of the base polymer compositions to meet the melting point requirements for the specific adhesive applications involved. However, the range of modifications permissible will vary depending on the base polyester selected and on the end-use application. We have found that by using polyester amides rather than polyesters, we gain an unexpected increase in resistance to organic solvents of the type used in dry cleaning processes such as perchloroethylene. This resistance to organic solvents is unexpected because the resulting compositions have an additional component and it would be expected to be a less crystalline material due to the introduction of such component in the polymer. Solubility of polymers in solvents is dependent to some extent on the crystallinity of the polymer. It is surprising that the polymers of our invention are not attacked by the solvents in question. By increased resistance, we mean that either the bonds have a higher bond strength than the corresponding polyester bonds or that the bonds prepared from the specific polyester amide composition resist the attack of solvents for a longer period of time than the unmodified polyester composition. The polyester amides are also more effective over a wider range of substrates than are the polyester adhesives.
Although we are not certain of the exact reason for this latter phenomenon, we believe that the possibilities for hydrogen bonding which exist in the polyester amide compositions are an important factor. Thus, the hydrogen atoms attached to the nitrogen atoms in the polyester amide chain can become attached via hydrogen bonds to sites in the substrate. The resulting bonds are then stronger and more solvent resistant than mere mechanical bonds in which chemical attractive forces are not involved.